Tamapin

The target of tamapin is the small conductance calcium-dependent potassium (SK) channel. This scorpion toxin blocks SK2 channels with selectivity for SK2 versus SK1 channels in a largely reversible manner.^[1] Despite completely different sequences, Apamin (a bee venom toxin) and tamapin share at least in part, the same binding sites on rat brain synaptosomes. Cloned SK2 are most sensitive for Apamin in binding assays and physiological recordings.^[1] However, tamapin displaces Apamin in binding assays and is therefore a stronger toxin with respect to Apamin. SK 1 and SK 3 are only affected with a high concentration of tapamin and therefore this toxin inhibits SK2 with the highest affinity, SK3 intermediate and the lowest affinity for SK1 channels.^[1] A less closely related member of the SK channels is the intermediate conductance calcium activated potassium channel SK4, also known as IK1, which is not sensitive to Apamin and is also not affected by Tapamin.^[1] The same applies to voltage dependent potassium channels; the block of SK2-mediated currents is not voltage dependent.^[1] This specific channel block evokes a reduction in the small conductance calcium-dependent potassium channels current.

Previous studies showed that the effect of tamapin is largely reversible and depends on time and concentration. The Indian red scorpion (Hottentotta tamulus) causes a large number of deaths annually especially among young children.^[3] Its venom contains highly specific potassium channel blockers such as iberiotoxin, which is a highly specific blocker of the high conductance calcium activated potassium channel, and tamulustoxin.^[4]